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11.
Predicting dry‐season flows with a monthly rainfall–runoff model: Performance for gauged and ungauged catchments 
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下载免费PDF全文 Hydrologic models are useful to understand the effects of climate and land‐use changes on dry‐season flows. In practice, there is often a trade‐off between simplicity and accuracy, especially when resources for catchment management are scarce. Here, we evaluated the performance of a monthly rainfall–runoff model (dynamic water balance model, DWBM) for dry‐season flow prediction under climate and land‐use change. Using different methods with decreasing amounts of catchment information to set the four model parameters, we predicted dry‐season flow for 89 Australian catchments and verified model performance with an independent dataset of 641 catchments in the United States. For the Australian catchments, model performance without catchment information (other than climate forcing) was fair; it increased significantly as the information to infer the four model parameters increased. Regressions to infer model parameters from catchment characteristics did not hold for catchments in the United States, meaning that a new calibration effort was needed to increase model performance there. Recognizing the interest in relative change for practical applications, we also examined how DWBM could be used to simulate a change in dry‐season flow following land‐use change. We compared results with and without calibration data and showed that predictions of changes in dry‐season flow were robust with respect to uncertainty in model parameters. Our analyses confirm that climate is a strong driver of dry‐season flow and that parsimonious models such as DWBM have useful management applications: predicting seasonal flow under various climate forcings when calibration data are available and providing estimates of the relative effect of land use on seasonal flow for ungauged catchments. 相似文献
12.
The feasibility of mangrove leaves as a full diet for sesarmid crabs has been questioned for decades. Since these leaves are nitrogen-poor, sesarmids probably obtain nitrogen from other sources to sustain growth. The aim of this study was to assess the food partitioning of the sesarmid species Neoepisesarma versicolor with emphasis on nitrogen allocation. The preference for animal tissue when crabs were pre-fed diets of different nitrogen content was determined in the laboratory. Furthermore, the possible in situ diet composition of N. versicolor was established from carbon and nitrogen stable isotope signature (δ13C and δ15N) of freshly caught individuals and their potential food sources, using a concentration-dependent mixing model. N. versicolor showed significantly higher feeding preferences for fish meat when pre-fed leaf material without than with access to meat, indicating that this crab species can meet its nitrogen demand by ingesting animal tissue. The stable isotope mixing model based on in situ materials suggests that the diet of N. versicolor consists of ∼60% leaves in terms of biomass, leaving ∼40% for other sources such as animal tissue and benthic microorganisms. The biomass contribution from animal tissues, in form of e.g. other crustaceans and fish carcasses, was found to account for ∼15%. Despite the relative low biomass fraction, animal food sources may contribute with up to half of the nitrogen in the diet of N. versicolor. The quantity of ingested sediment most likely exceeds that of animal tissues. However, due to the low concentration of assimilable microalgae and other microorganism, we propose that sediment associated sources are less important as a nitrogen source for N. versicolor than hitherto presumed. 相似文献
13.
We present a numerical method that incorporates particle sticking in simulations using the N-body code pkdgrav to study motions in a local rotating frame, such as a patch of a planetary ring. Particles stick to form non-deformable but breakable aggregates that obey the (Eulerian) equations of rigid-body motion. Applications include local simulations of planetary ring dynamics and planet formation, which typically feature hundreds of thousands or more colliding bodies. Bonding and breaking thresholds are tunable parameters that can approximately mimic, for example, van der Waals forces or interlocking of surface frost layers. The bonding and breaking model does not incorporate a rigorous treatment of internal fracture; rather the method serves as motivation for first-order investigation of how semi-rigid bonding affects the evolution of particle assemblies in high-density environments.We apply the method to Saturn’s A ring, for which laboratory experiments suggest that interpenetration of thin, frost-coated surface layers may lead to weak cohesive bonding. These experiments show that frost-coated icy bodies can bond at the low impact speeds characteristic of the rings. Our investigation is further motivated by recent simulations that suggest a very low coefficient of restitution is needed to explain the amplitude of the azimuthal brightness asymmetry in Saturn’s A ring, and the hypothesis that fine structure in Saturn’s B ring may in part be caused by large-scale cohesion.This work presents the full implementation of our model in pkdgrav, as well as results from initial tests with a limited set of parameters explored. We find a combination of parameters that yields aggregate size distribution and maximum radius values in agreement with Voyager data for ring particles in Saturn’s outer A ring. We also find that the bonding and breaking parameters define two strength regimes in which fragmentation is dominated either by collisions or other stresses, such as tides. We conclude our study with a discussion of future applications of and refinements to our model. 相似文献